1. Field of the Invention
This invention is generally related to tapers in optical fibers, and, more particularly, to a method and apparatus for using an etchant to achieve a desired taper in an optical fiber fluorescence probe.
2. Description of the Related Art
Conventional approaches to tapering fibers such as optical fibers (hereinafter "fibers") are not conducive to large scale production. Several prior approaches have included (a) slowly lowering a fiber into acid to obtain a taper over the desired area, and (b) immersing the region of the fiber to be tapered in an acid and slowly raising it out of the acid. A drawback to these approaches is that they require the fiber to be physically moved during the tapering procedure. During the etching process, even a small angular deviation from the vertical will distort the taper profile. Thus, the apparatus for lowering or lifting a fiber requires great precision and uniformity, especially when multiple fibers are etched simultaneously. It would be desirable to have a system for etching fibers that does not require the fibers to be moved. Another consideration is the safety hazard posed by open containers of acid when acid is used for tapering.
In a fiber optic based laser induced fluorescence sensor (LIFS) probe, a coherent energy field propagates through a fiber to an active region. In the active region, evanescent field excitation leads to a fluorescent signal from an analyte outside the fiber. The fluorescent signal propagates back through the fiber and is used to estimate the concentration of the analyte. The performance of a fiber optic LIFS probe depends on the strength of the evanescent field, the strength of the fluorescent signal returned from the probe, and the number of fluorophores which adhere to the sensor. One approach to enhancing the sensor has been to taper the probe.
The need for precision tapering extends to applications other than the LIFS probe context, which may require individualized taper shapes. Methods for linear and step tapers have been disclosed, but these are only several of the many taper shapes which may be needed for various applications.